1. Field of the Invention
The present invention relates to powder metal forgings and the manufacture thereof, and, more particularly, to powder metal forgings having a helical outer contour or profile, and an inside contour.
2. Description of the Related Art
In the manufacture of near net shape parts, for example a helical gear or inner race of a constant velocity joint (CVJ), one method of manufacture is a wrought forging process that provides near net shaped parts, which requires precision blanks machined prior to the forging process. Further, in the case of wrought forged gears or a CVJ inner race, or other part, which may have an inside diameter, the inside diameter must be pierced, which is additional material waste and cost.
A method and apparatus is known for producing in a single stroke a forged metal article with a helical contoured surface. The apparatus uses an upper punch with a generally smooth surface which is telescopically received in a punch housing and a lower punch of generally smooth surface which is mounted for free rotation with respect to the axis of the die assembly. However, this process provides a simple tooling arrangement for forging pinions with no inside diameter present. Further, there can be considerable flash formed on the part as a result of the single stroke simultaneously closing the dies and compressing the preform with the punch.
During powder metal forging, there is considerable force upward that tends to separate the upper die from the lower die and allows a shoulder to form on the part instead of a thin flash parting line. In the case of gear manufacturing this undesirable movement of the tool member causes lower density in the teeth and non-fill of the tooth form. More material and tonnage is required to fill the teeth in the part, but also allows for the formed shoulder (flash) to become larger as a result. This additional material is required to be machined off as a secondary process along with the inside diameter since there is no provision in this process to form the inside diameter in the forging process. The result is wasted material and additional processing which drives up cost. This old method also uses very weak upper tooling where the outer punch can be prone to cracking in some gear configurations.
What is needed in the art is a powder metal forging and method and apparatus of manufacture, and powder metal forgings manufactured therefrom, which produces a powder metal forging with a helical outer profile and an inside contour.